I don't think they'll give a big explanation for why he wasn't present. It was beyond his league. In the end the army were unable to cope.

In the IM3 prequel comics, Tony sent Rhodey into Hong Kong to investigate a lead into the Ten Rings organization. It turned out to be a trap, which WM/Rhodey handled and eventually got to New York but only in time to watch the Avengers in the shawarma shop. I'm not sure if they'll touch on this but maybe in passing they will.